Testing vapor recovery systems

ABSTRACT

A method of leakage testing a volatile liquid tank farm together with a vapour recovery system, to collect vapour from the tanks at the time of re-filling them with volatile liquid. The tank farm has individual fill-pipes ( 13 ) for each tank ( 10 ) with each fill-pipe outlet below the normal minimum liquid level in the tank and each tank having a vent-pipe ( 11 ) connected to a common manifold ( 25 ). To perform the test, the common manifold is closed to atmosphere and one side of a shut-off valve ( 17 ) is connected to the manifold ( 25 ), a flow meter ( 20 ) being connected to the other side of the shut-off valve. Flow meters ( 22, 23 ) are coupled to all but one of the fill-pipes ( 13 ), the shut-off valve ( 17 ) is opened to allow volatile liquid to be supplied to the remaining fill-pipe so as to increase the volume of volatile liquid in the associated tank, and the out-flow of gas or wet vapour from the common manifold ( 25 ) is monitored via the flowmeters ( 20, 22, 23 ) for substantial correlation to the volume of volatile liquid admitted into the tank associated with the remaining fill-pipe. The method can be modified also to allow the testing of individual tanks of a tank farm, where the vent pipes of the tanks individually vent to atmosphere, with the leakage test or vapour recovery system test then being performed one at time, on each of the individual tank(s).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage application of InternationalApplication PCT/GB00/00616, filed Feb. 21, 2000, which internationalapplication was published on Aug. 31, 2000 as International PublicationWO00/50334 in the English language. The International Application claimspriority of Great Britain Patent Application 9904030.5, filed Feb. 22,1999.

BACKGROUND OF THE INVENTION

This invention relates to a method of testing a vapour recovery systemassociated with a tank for a volatile liquid, such as a tank for holdingpetroleum spirit (hereinafter referred to simply as “spirit”) asinstalled at a fuel filling station for motor vehicles. The inventionfurther relates to a method of testing a vapour recovery system of atank farm, comprising a plurality of such spirit tanks, and a method oftesting a tank installation.

Historically, a spirit tank at a fuel filling station had a simplevent-pipe, leading to atmosphere. This allowed vapour displaced from thetank during a refilling operation to be vented to atmosphere. Betweendeliveries, the vent-pipe allowed natural venting of the tank to takeplace as well as the ingress of air upon spirit being withdrawn from thetank, to be dispensed through a fuel delivery pump.

To overcome the problem of environmental pollution consequent upon thisnatural venting process, spirit tank farms have been, and are being,modified in various ways to operate on a current standard known as Stage1B, where vapour displaced from a tank during a delivery process isreturned to a road tanker delivering the spirit. A typical modificationis to connect all of the individual spirit tank vent-pipes to a commonmanifold which has a single vent-pipe fitted with a pressure/vacuumvalve (referred to hereinafter as a “p/v valve”), or sometimes aplurality of vent-pipes each fitted with a p/v valve. A p/v valve isnormally closed but opens if the pressure in the manifold to which it isconnected falls below a pre-set sub-atmospheric value, caused bydispensing spirit, or if the pressure rises above some other pre-setvalue above atmospheric.

When spirit is to be loaded into one or more of the tanks, the commonmanifold is connected to a vapour recovery system on the delivery roadtanker, and the spirit vapour is drawn back into the tanker to beprocessed back to liquid spirit. In this way, much of the vapourpreviously released to atmosphere can be prevented, at the time ofrefilling the tanks of a filling station.

In the United Kingdom, at the present time it is a legal requirement tohave all vapour recovery systems at retail petrol filling stationsregistered with the appropriate authority. Shortly it will be arequirement that such a system is tested to ensure that the systemoperates correctly, efficiently and safely with any leaks falling withinthe low limits set within European guidelines.

BRIEF SUMMARY OF THE INVENTION

The present invention aims at providing a method of testing one or moretanks intended to hold spirit, firstly to ensure that the installationis suitable for the fitting of a vapour recovery system and secondly,once such a vapour recovery system has been installed, that the systemis operating correctly, efficiently and safely, with no significantleaks that would prevent the recover system from operating correctly,efficiently and safely.

According to a first aspect of the present invention, there is provideda method of testing a volatile liquid tank installation having afill-pipe projecting downwardly into the tank with the fill-pipe outletbelow the normal minimum liquid level in the tank and the tank alsohaving a vent-pipe, in which method one side of a shut-off valve isconnected to the vent-pipe, a flow meter is connected to the other sideof the shut-off valve, said valve is opened, liquid is supplied to thetank so as to increase the volume of liquid therein, and the out-flow ofgas or wet vapour from the vent-pipe is monitored for substantialcorrelation to the volume of liquid admitted to the tank.

It will be appreciated that this method permits the testing ofindividual spirit and/or diesel tanks as installed for example at a fuelfilling station, where those tanks are naturally vented as has beendescribed above, prior to the fitting of a vapour recovery system suchas that known in the UK as a Stage 1B system. By monitoring the volumeout-flow of vapour from the vent-pipe for a substantial correlation withthe volume in-flow into the tank, and preferably also the vapour flowrate and time of out-flow, for comparison with the time and in-flow ofliquid fuel, there can be a reasonable assurance that there is nosignificant leak, permitting the escape to atmosphere of the vapour,from some other point in the installation. If the correlation fallsoutside expected limits, a leak, blockage or restriction may besuspected and a suitable investigation commenced.

Advantageously, a pressure gauge is arranged to sense the pressure inthe vent-pipe, liquid is supplied to the fill-pipe so as to increase thevolume of liquid in the tank, and the shut-off valve is operated tocontrol the build-up of pressure in the vent-pipe up to some maximumvalue, consequent upon the displacement of vapour or wet vapour from thetank. At the completion of the delivery of liquid to the tank, theshut-off valve is closed and the subsequent decay of the pressure in thevent-pipe is monitored. By monitoring this decay, it is possible todetermine whether there are leaks; and by taking into account thevarious relevant parameters (such as tank volume, ullage space, startingpressure and so on), then the seriousness of a suspected leak may beassessed.

Preferably, the testing is performed in the above order—that is to say,the out-flow of vapour on supplying liquid to a tank is checked prior totesting for the decay in pressure allowed to build in the vent-pipe,when the valve is closed.

Even prior to performing the test described above, a preliminary stepmay be performed, in which the shut-off valve is closed and the pressurewithin the vent-pipe is monitored as liquid is drawn from the tank. Suchdrawing of liquid may be in the course of the filling of the tanks ofmotor vehicles and should create a negative pressure in the vent-pipe;this part of the test will also serve to ensure that there are no, oronly minimal leaks.

Once, the individual tanks have been tested and found to comply withinthe permitted pre-set limits, the Stage 1B vapour recovery system may beinstalled. Then, that implementation may be tested for compliance and itis recommended that the installation is tested periodically forcontinuing compliance, typically once every twelve months.

According to a second aspect of this invention, therefore, there isprovided a method of testing a vapour recovery system installed at avolatile liquid tank farm comprising a plurality of volatile liquidtanks each having an individual fill-pipe projecting downwardly into thetank with the fill-pipe outlet below the normal minimum liquid level inthe tank and each tank having a vent-pipe coupled to a common manifold,in which method the common manifold is closed to atmosphere and one sideof a shut-off valve is connected to the manifold, a flow meter isconnected to the other side of the shut-off valve, flow meters arecoupled to all but one of the fill-pipes, said shut-off valve is opened,liquid is supplied to the remaining fill-pipe so as to increase thevolume of liquid in the associated tank, and the out-flow of gas of wetvapour from the common manifold is monitored for substantial correlationto the volume of liquid admitted to the tank associated with saidremaining fill-pipe.

Preferably, a pressure gauge is arranged to sense the pressure in themanifold, liquid is supplied to said remaining fill-pipe so as toincrease the volume of liquid in the associated tank, the shut-off valveis operated to control the build-up of pressure in the manifoldconsequent upon the displacement of gas or wet vapour from the tank, theshut-off valve is closed upon the completion of the supply of liquid tothe tank, and the subsequent decay of the pressure in the manifold ismonitored. In the alternative, the shut-off valve need not be closeduntil all tanks have been supplied with liquid, the decay then beingmeasured for the whole system, at the very end of the testing procedure.

In a Stage 1B vapour recovery system, the common, manifold is fittedwith one or more p/v valves. For such a case, the vacuum operation ofthe p/v valve should be tested before the performance of the testingmethod, by having the shut-off valve closed and checking for a negativepressure in the manifold. The pressure side of the p/v valve may bechecked later, again with the shut-off valve closed, and allowingpressure to build until the p/v valve opens—which normally should be at35 mbar, for the systems currently in use.

With a Stage 1B system, vapour displaced from a spirit tank by incomingfuel into that tank is recovered by being drawn back to the deliverytanker from the manifold, and this relies on the tanker generating asub-atmospheric pressure to draw the vapour. For this purpose, a hose isarranged to connect the other side of the shut-off valve to a vapourrecovery system (such as on a tanker), and a pressure gauge is arrangedto sense pressure in that hose, to test for a sub-atmospheric pressuregenerated by the vapour recovery system, such as on the tanker.

For a multi-tank farm, the testing method should be repeated for eachtank of the Farm, with liquid being supplied to the different tanksduring each performance of the testing method. Repeated performance ofthe testing method may be effected by transferring a flow meter from onefill-pipe to another and then supplying the liquid to the pipe fromwhich the flow meter was removed, and monitoring for out-flow of gas orwet vapour from the other fill-pipes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

In order that the invention may better be understood, two specificexamples of testing method of this invention will now be described indetail, reference being made to the accompanying drawings, in which:

FIG. 1 diagrammatically represents a tank farm having naturally ventedtanks, in the course of being tested;

FIG. 2 is similar to FIG. 1, but of a tank farm fitted with a Stage 1Bvapour recovery system;

FIG. 3 is a diagrammatic cross-section through an underground tank of atank farm;

FIG. 4 is a diagrammatic vertical section through a filling assembly fora tank, showing possible leaks; and

FIG. 5 is a cut-away view on an enlarged scale of a tank T-piecetogether with a fill-pipe.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1, there is shown a tank farm having aplurality of underground spirit tanks 10A, 10D, 10C and 10D, each havingits own individual vent-pipe 11A, 11B, 11C and 11D. Each vent-pipe leadsfrom an upper portion of the respective tank and has a simple weathercap 12 feted to the free upper end of the pipe. Each tank 10A . . . 10Dhas a respective relatively large diameter fill-pipe 13A . . . 13D,which fill-pipe leads to a lower portion of the respective tank. All ofthe upper ends of the fill-pipes are usually arranged in a close group(as shown), for easy access by a road tanker such as that illustrated at14, delivering fuel to the tank farm.

The tanker 14 is fitted with a vapour recovery mechanism, whereby vapourdriven from the ullage space of a tank during the filling of that tankmay be drawn back into the tanker, to be processed to liquid fuel andre-used. For a naturally vented system as illustrated in FIG. 1, thedelivery tanker's vapour recovery mechanism is not normally used. Thedelivery tanker “breathes” by its own p/v valves fitted to the top ofeach delivery compartment (pot). The storage tank, on receiving incomingfuel vents to atmosphere vapour driven from the tank through thevent-pipe. Fuel delivery is performed by connecting a flexible hose 15from a pot of the tanker to a fill-pipe, and then opening the associateddelivery valves on the tanker.

in the arrangement shown in FIG. 1, tank 10D is intended to hold dieselfuel. A flexible hose 16 is connected to the spirit tank vent-pipe 11A,after removing the weather cap 12 therefrom, that flexible hose 16connecting to one side of a shut-off valve 17, mounted on a stand. Thevent-pipe side of that valve is provided with a pressure/vacuum gauge18, to sense the pressure prevailing in the associated vent-pipe.

The other side of the shut-off valve 17 is connected by a further hose19 to the vapour recovery mechanism of the tanker 14, through a volumeflow meter 20 and a further pressure/vacuum gauge 21. During off-loadingof diesel fuel into tank 10D, the vacuum (negative pressure) created bythe delivery tanker can be monitored on gauge 21. Then, at the start ofa spirit drop into tank 10A, the fill-pipe for the diesel tank 10D issealed, and the fuel pipes 13B and 13C of the other two spirit tanks arefitted with respective flow meters 22 and 23.

The installation of the flexible hose 16 and shut-off valve 17 may becompleted prior to the arrival of the tanker 14, on site. The shut-offvalve 17 must be in the closed position before connection to the tankerthrough hose 19, during which time the pressure/vacuum gauge 18 may beused to monitor the pressure fall in vent-pipe 11A as fuel is drawn fromtank 10A, on filling motor vehicles attending the filling station. Thispressure/vacuum gauge 18 will show that the pressure in the vent-pipe isfalling, and remains low, as more and more fuel is drawn from the tank.

When the tanker arrives on site, it is connected to fill-pipe 13A byflexible hose 15 and to the shut-off valve 17 by flexible pipe 19, asdescribed above. The valve 17 is opened and the vapour recovery systemof the tanker operated; the pressure/vacuum gauge 21 will show whetherthe tanker's vapour recovery system is producing a suitablesub-atmospheric pressure for vapour recovery. Upon commencement of thedumping of fuel into tank 10A, a corresponding out-flow of vapour, orwet vapour, may be checked by the flow meter 20. Moreover, the flowmeters 22 and 23 may also be checked, to ensure there is neither in-flownor out-flow whilst tank 10A is being filled. Apart from possiblepipe-work errors, this will also check for correct labelling of thevent-pipes.

Finally, the valve 17 is partially dosed and then operated asappropriate to prevent an excessive build-up of pressure in thevent-pipe as the dumping of spirit into the tank 10A continues, usinggauge 18 to check the pressure. At the completion of the delivery, thevalve 17 is closed and then the decay of pressure in tie vent-pipe ismonitored, on gauge 18. If the pressure does not decay in the expectedway (i.e. a small initial pressure drop whereafter the pressurestabilises), the presence of leaks must be presumed.

The above procedure is repeated for all three tanks and provided theobtained results ate within acceptable (but very low) limits, then aStage 1B vapour recovery system may be installed. This is shown in FIG.2, during the course of testing, and like parts of those of FIG. 1 aregiven like reference characters and will not be described in detailagain, here.

As can be seen in FIG. 2, the three vent-pipes 11A, 11B and 11C areconnected to a common manifold 25, having a single atmospheric vent-pipe26 fitted with a p/v valve 27, which valve is arranged to open, and sovent the manifold to atmosphere, should the pressure within the manifoldfall below or exceed a pre-set limit. So long as the pressure in thevent-pipe remains inside those limits, the p/v valve will remain closed.The manifold 25 moreover has a common connection 28 for the vapourrecovery system of the tanker 14.

Below, the precise steps to be followed in a specific example of Stage1B vapour recovery are set out. Here, the system is described in moregeneral and broad terms.

To perform a method of this invention, the shut-off valve 17 on itsstand is coupled to connection 28 by flexible hose 16, and also to thetanker by hose 19, as described above. The shut-off valve 17 is openedand the vapour recovery system of the tanker operated as fuel is dumpedin the tank 10A; the flow of vapour through pipe 19 may be monitored onmeter 20, and should fall within a range broadly comparable to thevolume delivery of fuel into tank 10A. Moreover proper operation of thevapour recovery system on the tanker may be monitored by pressure gauge21. The valve 17 may be closed temporarily at the start of a fueldumping, to check there is a fall in pressure at gauge 21, so confirmingthe tanker's vapour recovery system is working.

The valve 17 is then closed as fuel continues to be dumped into tank10A. Relatively short periods of fuel flow are dumped from differentcompartments (pots) of the tanker, one at a time, into each tank insequence to allow the reaction time of vapour flow rates and the actualflow rates to be registered on gauge 20. By supplying fuel in sequenceand for only a short period to each tank, the corruption of data isavoided and which otherwise could happen if each tank received its fullload in one drop, for the tank farm would then become progressivelycharged with excessive vapour pressures, making the readings more andmore inaccurate.

When the remainder of the fuel in the pot of the tanker is dumped intothe first tank 10A, the ullage space of that tank will gradually bedistributed across the ullage spaces of the other tanks and so a muchlower rise in pressure may be anticipated. Further, a more rapid raisein pressure can be anticipated when loading fuel into the other tanks,again depending upon the volumes already in the tanks. The valve 17 isoperated as appropriate to prevent an excessive build-up of pressure inthe manifold as the dumping of fuel into the tank 10A continues, usinggauge 18 to check the pressure. At the completion of the entire deliveryto all the spirit tanks, the valve 17 is closed and then the decay ofpressure in the manifold 25 is monitored, on gauge 18. If there is anexcessive pressure decay (say more than 6 mbar over a 6 minute period),the presence of leaks can be presumed. Moreover, if there is an out-flowof vapour from either fill-pipe 13B or 13C, as determined by flow meter22 or 23, it may be presumed that there is leakage at the connectionbetween the fill-pipe and tie tank itself.

FIG. 3 illustrates a portion of an underground spirit tank including amanhole and lid, through which the fill-pipe passes As can be seen, thetank has a neck 30 fitted with a lid 31, the lid being disposed in amanhole 32 below the ground surface 33. The fill-pipe has a connectionflange 34 at its free end above the ground, the pipe then passingthrough a side wall of the manhole and being connected to a T-piece 35fitted to the tank lid. Below the lid, the fill-pipe extends downtowards the bottom of the tank. Also shown in FIG. 3 is a gauge probe 37and a vent-pipe 38.

FIGS. 4 and 5 show in more detail the construction at the tank lid 31. Atank lid nipple 39 is threaded into a threaded opening in the tank lid31, and T-piece 35 is threaded on to that nipple. A flanged drop tube 40passes through the nipple 39, a seal being effected between the flange41 of the drop tube 40 and the nipple 39 by means of an O-ring 42. Thedrop tube is held down on to the O-ring by means of a drop tuberetaining cage 43 having a lower pressure member 44 bearing on theflange 41 of the drop tube and a threaded ring 45 engaged with thethreads in the upper part of the T-piece. By rotating ring 45, thepressure on the drop tube seal may be increased, to the required level.

The upper part of the T-piece is closed by a plug 46. The lower end ofthe drop tube 40 is connected to an overfill prevention valve 47, thelower end of which is connected to the lower portion of the fill-pipe48, descending to the bottom of the tank.

As shown in FIG. 4, liquid or vapour leakage may occur at several of thejoints described above and as illustrated by arrows A (the lower portionof the fill-pipe/overfill prevention valve connection 48/47), B (theoverfill prevention valve/drop tube connection 47/40) and C (the droptube/nipple connection 40/39). Moreover, leakage can occur at the tanklid/nipple connection 31/39, or the plug/T-piece connection 46/35.

It will be appreciated that the testing procedures described above allowproper and complete testing of a tank farm, initially when operating asa simple naturally vented system, and subsequently when a Stage 1Bvapour recovery system has teen installed.

The full procedure to be followed in performing a complete Stage 1Bvapour recovery system testing method will now be described in detail,referring to FIGS. 1 and 2.

1. Set up test equipment as shown in FIG. 2. Valve 17 is shut. Hose 16is connected to site vapour recovery connection 28.

2. Delivery tanker arrives on site. Hose 19 is connected, one end to thetanker and the other end to valve 17.

3. The vacuum side of the p/v valve 27 is checked for correct operationwith valve 17 shut; any negative pressure in the tank farm will registeron gauge 18. A negative pressure will be caused by sales of petrol atthe pumps and will indicate that the vacuum side of the p/v valve 27 isoperating correctly.

4. Deliver hose 15 is connected to the diesel tank 10D at the fill pointat the top of the fill-pipe 13D. Valve 17 is shut and as diesel isdumped into tank 10D, a negative pressure should be created within thetankers hose 19 and registers on gauge 21. This should be registeringaround −20 mbar if the tanker's vapour recovery equipment is operatingcorrectly.

5. Dumping of the whole tanker compartment (pot) of diesel to be dumpedis timed. This is the Total Pot Delivery Time (TPDT), in minutes andseconds.

6. Valve 17 is opened during the delivery of diesel to check again thecorrect operation of the vacuum side of the p/v valve 27.

7. The TPDT measured for this diesel pot is a convenient benchmarkagainst which to measure the TPDT of all the other pots, diesel willnormally off-load at a slower rate than spirit.

8. After diesel has finished, hose 15 is connected to tank 10A at thefill point at the top of fill-pipe 13A, and with valve 17 open, spiritis released from the tanker into tank 10A. This will promote vapour toflow through vent 11A and the Reaction Time (RT) is measured from whenfuel is released from the tanker until vapour flow reaches gauge 20.This measured amount of time (usually in seconds) will be known as theinitial Reaction Time (IRT). The maximum vapour flow rate (MFR) on gauge20 and also the Time to reach Maximum Flow Rate (TRMFR) are assessed.The delivery of fuel into tank 10A is halted after 1 minute. This is thefirst stage drop completed for tank 10A.

9. The hose 15 is transferred to the fill point of tank 10B at the topof the fill-pipe 13B and to the correct fuel pot faucet on the tanker.The process is then repeated with fuel being dumped from another pot onthe tanker into tank 10B. The IRT, MFR and TRMFR are then measured forthis pot and fuel delivery halted after 1 minute The period of 1 minuteis normally more than sufficient time to obtain all relevant readings,but should continue as long as necessary to get all the readings andmake a note of the time taken.

10. The hose 15 is then transferred to the fill point of tank 10C at thetop of the fill-pipe 13C and the process repeated again, with fuel beingdumped from another pot on the delivery tanker.

11. With regard to a site configuration as in FIG. 1, the followingreadings are obtained:

TPDT for the diesel tank 10D in minutes and seconds.

IRT for the spirit tanks 10A, 10B, 10C in seconds.

MFR for the same 3 tanks, in litres of vapour flow per minute.

TRMFR for the same 3 tanks, in seconds.

The tine of the first stage drop for each spirit tank (normally 1minute).

12. Analysing the above times and flow rates for the different tanks andcomparing them with one another, will highlight the characteristics thatare likely to cause faults within the site's vapour recovery system. Forexample, if all the tanks are positioned very close together on theforecourt, we might expect all the readings to be similar. If howeverone tank has a very slow IRT and TRMFR and a very low MFR as compared tothe others, this is likely to indicate some form of blockage orrestriction in the vent-pipe 11 of that tank.

13. The hose 15 is then reconnected to the fill point on tank 10A andthe correct pot faucet on the tanker, for the second stage of the drop.Dumping of the remainder of fuel in that pot is timed and added to thetime of the first stage (normally 1 minute), to give the TPDT for eachtank. To calculate the delivery rate for each pot, the volume of fueloff-loaded in each pot is divided by TPDT. This figure (inlitres/minute) should relate closely to the maximum vapour flow rateregistered on gauge 20.

14. During the dumping of fuel from each pot, the valve 17 is brieflyshut to check that either a negative pressure or a pressure drop ongauge 21 is registered. This will indicate that the p/v valve located ontop of that pot on the delivery tanker is operating correctly.

15. During the second stage of off-loading fuel into each of the spirittanks 10A, 10B, 10C, it is necessary to use two or more hosessimultaneously, connected to the respective tanker pot and tank, tomeasure the combined vapour flow rate through the manifold 25. This willregister on gauge 20. This reading (litres/minute) enables the analysisof the characteristics of any blockage or restriction in the manifold.

16. Once this “Dual Flow Rate” has been measured, valve 17 is partiallyclosed whilst fuel is still off-loading into the tanks. This allows thebuild-up and maintenance of a steady pressure within the site's Stage 1Bvapour recovery system.

17. While this pressure is building up and being monitored on gauge 18,flow rate gauges 22 and 23, are fitted on to the fill point connectionat the top of fill-pipes 13B and 13C (not shown on FIG. 2). These gaugesare shut before being fitted.

18. When the pressure in the vapour recovery system has reached and ismaintained at just below the release pressure of the p/v valve 27(normally 35 mbar), the flow rate gauges 22 and 23 are opened and theindicator needle allowed to settle. Any leaks from the fill-pipes 13Band 13C will register as a continuous and steady flow rate on thesegauges. This process is repeated on all the fill points of all thespirit tanks as the hose 15 is swapped around from tank to tank.

19. While the second stage drop of the very last pot is beingoff-loaded, valve 17 is shut fully to build up pressure in the system inorder to check the release pressure of the p/v valve 27. The build up ofpressure is monitored on gauge 18 and at or around 35 mbar, the p/vvalve should activate and open, temporarily releasing the pressure andvapour to atmosphere. If the p/v valve is operating correctly, theneedle on gauge 18 will rapidly fluctuate up and down, as the p/v valveopens and loses in surges. (It can easily be heard opening and closingrapidly and it should be easy to see vapour escaping from it). If it isnot operating correctly, the needle on gauge 18 will continue to risewell beyond 35 mbar, indicating that the valve has stuck down shut. Thewhole valve will need to be replaced if either its pressure or vacuumsides are not operating correctly. The valve will also be deemed faultyif it opens prematurely at below 35 mbar.

20. Once this has been checked, valve 17 is partially opened to maintaina steady pressure in the system just below the release pressure of thep/v valve 27. To maintain a constant pressure will require continuousattention to gauge 18 and minor adjustment of the valve 17 until thevery last pot of fuel has been completed. The valve 17 is then shutimmediately, locking in this pressure within the Stage 1B vapourrecovery system.

21. This pressure reading of just under 35 mbar on gauge 18 will decayslightly for a short period of time as the fuel in the tank settles. Thepressure should then remain stable at around 30 mbar. Any significantdecay in pressure (over a 10 mbar drop) over the next 6 minutes willindicate the presence of leaks within the system.

22. With valve 17 shut, the tanker driver has completed the off-loadingand disconnects the delivery hose 15 end vapour recovery hose 19 and canleave the site.

23. Hose 16 is then disconnected from vapour recovery connection valve28 that should then automatically shut tight. Another flow meter gauge(similar to 22 and 23) is fitted to a cap connected to valve 28. Beforebeing fitted, the gauge is shut. After a short period, the flow rategauge is opened and the indicator needle allowed to settle. Anycontinuous flow registering on this gauge will indicate that the vapourrecovery connection valve 28 is faulty and will need to be replaced.

24. The Stage 1B vapour recovery test is now complete. All that remainsis to analyse the test results and prepare the report.

What is claimed is:
 1. A method of leakage testing a volatile liquidtank installation having a fill-pipe projecting downwardly into the tankwith the fill-pipe outlet below the normal minimum liquid level in thetank and the tank also having a vent-pipe, in which method one side of ashut-off valve is connected to the vent-pipe, a flow meter is connectedto the other side of the shut-off valve, said method involving the stepof as said valve is opened, volatile liquid is supplied to the tank soas to increase the volume of volatile liquid therein, and the out-flowof gas or wet vapour from the vent-pipe is monitored via said flow meterfor substantial correlation to the volume of volatile liquid admitted tothe tank.
 2. A method of testing as claimed in claim 1, in which thereaction time of the out-flow of gas or wet vapour to register on agauge associated with said shut-off valve is also monitored.
 3. A methodof testing as claimed in claim 2, in which said reaction time ismonitored from the commencement of liquid supply to the tank.
 4. Amethod of testing as claimed in claim 1, in which a pressure gauge isarranged to sense the pressure in the vent-pipe, liquid is supplied tothe fill-pipe so as to increase the volume of liquid in the tank, theshut-off valve is operated to control the build-up of pressure in thevent-pipe consequent upon the displacement of vapour or wet vapour fromthe tank.
 5. A method as claimed in claim 4, in which the shut-off valveis closed upon the completion of the supply of liquid to the tank, andthe subsequent decay of the pressure in the vent-pipe is monitored.
 6. Amethod of testing as claimed in claim 1, in which the shut-off valve isclosed and pressure within the vent-pipe is monitored as liquid is drawnfrom the tank, as a first step of the testing method.
 7. A method asclaimed in claim 6, in which the vent-pipe is fitted with at least onepressure/vacuum valve (p/v valve) arranged to limit the maximum andminimum pressures in the vent-pipe.
 8. A method of leakage testing avolatile liquid tank farm comprising a plurality of tanks each having anindividual fill-pipe projecting downwardly into the tank with thefill-pipe outlet below the normal minimum liquid level in the tank andeach tank having a vent-pipe coupled to a common manifold, in whichmethod the common manifold is closed to atmosphere and one side of ashut-off valve is connected to the manifold, a flow meter is connectedto the other side of the shut-off valve, a plurality of flow meters arecoupled to all but one of the fill-pipes, said method involving the stepof as said shut-off valve is opened, a volatile liquid is supplied tothe remaining fill-pipe so as to increase the volume of volatile liquidin the associated tank, and the out-flow of gas or wet vapour from thecommon manifold is monitored via said flow meter for substantialcorrelation to the volume of volatile liquid admitted to the tankassociated with said remaining fill-pipe.
 9. A method as claimed inclaim 8, in which liquid is supplied simultaneously to two tanks for apart of the overall testing method, the combined out-flow of gas or wetvapour being monitored during this time.
 10. A method as claimed inclaim 8, in which the shut-off valve is closed during the start of thesupply of liquid to a tank, and the pressure in the common manifold ismonitored to test for leaks at the fill-pipes of the other tanks.
 11. Amethod as claimed in claim 5, in which a pressure gauge is arranged tosense the pressure in the manifold, liquid is supplied to said remainingfill-pipe so as to increase the volume of liquid in the associated tank,the shut-off valve is operated to control the build-up of pressure inthe manifold consequent upon the displacement of gas or wet vapour fromthe tank.
 12. A method as claimed in claim 11, in which the shut-offvalve is closed upon the completion of the supply of liquid to all ofthe tanks, and the subsequent decay of the pressure in the manifold ismonitored.
 13. A method as claimed in claim 8, in which the flow meterscoupled to said all but one fill-pipe are monitored for the out-flow ofgas or wet vapor as liquid is supplied to said tank and the build-up ofpressure is controlled by operation of the shut-off valve.
 14. A methodof testing as claimed in claim 8, in which the pressure within thecommon manifold is monitored as liquid is drawn from the tank, as afirst step of the testing method and before liquid is supplied to thetanks.
 15. A method as claimed in claim 8 and wherein the commonmanifold is fitted with a pressure/vacuum valve arranged to vent themanifold to atmosphere whenever the pressure differential between thatin the common manifold and atmosphere exceeds a predetermined value, inwhich method the normal operation of the pressure/vacuum valve ischecked by operation of the shut-off valve during the performance of thetesting method.
 16. A method as claimed in claim 8, wherein the testingmethod is repeatedly performed by transferring a flow meter from onefill-pipe to another and then supplying liquid to said one fill-pipe andmonitoring for out-flow of gas or wet vapor from the other fill-pipes.17. A method as claimed in claim 1, for use in conjunction with a fueldelivery tanker having a vapor recovery system, in which a hose isarranged to connect the other side of said shut-off valve to the fueldelivery tanker's vapor recovery system, and a pressure gauge isarranged to sense pressure in that hose, to test for correct operationof the vapor recovery system.
 18. A method as claimed in claim 8, foruse in conjunction with a fuel delivery tanker having a vapor recoverysystem, in which a hose is arranged to connect the other side of saidshut-off valve to the fuel delivery tanker's vapor recovery system, anda pressure gauge is arranged to sense pressure in that hose, to test forcorrect operation of the vapor recovery system.